Silicon-based semiconductor devices are used in a variety of products indispensable in modern life, including computers, mobile phones, smartphones, automobiles, refrigerators, communication devices and military and aerospace industries.
Monosilane is used to form a polycrystalline silicon thin film in a semiconductor process and an amorphous silicon thin film of a solar cell. As degree of integration of semiconductor devices increases and the so-called linewidth decreases more and more, it becomes difficult to fabricate silicon films with monosilane. In contrast, it is reported that silicon thin films can be formed with disilane or higher silanes at lower temperature or at higher speeds of up to about 20 times at the same temperature because the decomposition temperature is lower than that of the monosilane. Thus, grown silicon thin film is reported to have superior resistance. Accordingly, demand on disilane is increasing gradually as the linewidth of semiconductor devices become narrower. However, disilane costs hundreds times more per unit weight as compared to silane. Therefore, a process allowing production of the commercially valuable disilane in large scale will provide economic advantages to producers of silane, expand application of disilane, and lower the price of semiconductor components and devices fabricated using disilane.
At present, several techniques are available for production of disilane. Hydrolysis of magnesium silicide developed as a process for producing monosilane is not used to produce monosilane anymore because of low competitiveness. Although disilane is produced as a byproduct, this process is not suitable for large-scale production of disilane since a large quantity of silane is accompanied. Disilane is also prepared from hexachlorodisilane or hexaethoxydisilane in a solvent using a reducing agent such as lithium aluminum hydride (LiAlH4). Although the yield of disilane is high, this process is not used for commercial purposes since the starting material, hexachlorodisilane and the reducing agent are expensive and it is difficult to separate the organosilicon compounds produced as a byproduct. Another method of producing disilane is the electric discharge method. Although it is reported that disilane can be obtained with a high yield of 80% or greater, this method has not been commercialized yet because of the difficulty of development of a commercial-scale production apparatus. Another method is to produce disilane from monosilane using a catalyst. For example, monosilane is contacted with an alumina catalyst or a mixed oxide catalyst comprising alumina at 50-400° C. Although the yield of disilane is relatively high, this method requires long reaction time and the reaction rate is not as high as that of a catalytic reaction. In addition, unless the reaction condition is controlled adequately, monosilane may be excessively decomposed on the surface of the catalyst having a large surface area, leading to production of polysilane powder. This pyrolysis-based method also focuses on minimizing the generation of solid particles.
The above-described methods focus on preparation of higher silanes with three (3) to seven (7) silicon atoms from monosilane with less waste of the monosilane. However, they are not suitable for maximizing production of costly higher silanes from relatively inexpensive monosilane. For large-scale production of disilane and higher silanes, an economically effective preparation method is required.